There are two containers X and Y. X contains 100 ml of milk and Y contains 100 ml of water. 20 ml of milk from X is transferred to Y. After mixing well, 20 ml of the mixture in Y is transferred back to X. If m denotes the proportion of milk in X and n denotes the proportion of water in Y, then which one of the following is correct?

After 20 ml of milk transferred from container X to container Y, Milk in container X = 100 – 20 = 80 ml
Amount of solution in container Y becomes = 100 ml water + 20 ml milk = 120 ml

Ratio of milk in container Y solution = 20 : 120 = 1 : 6
By corollary, ratio of water in Y solution = 5 : 6 (100 : 120)

After 20 ml of milk transferred from container Y to container X, Milk in container X = 80 + 1/6 *20 = 83.33 ml
Amount of water in Y = 5/6 * 100 = 83.33 ml

Thus, m = n